A vacuum cleaner typically comprises a main body containing dirt and dust separating apparatus, a cleaner head connected to the main body and having a suction opening, and a motor-driven fan unit for drawing dirt-bearing air through the suction opening and the cleaner head, and into the main body. The suction opening is directed downwardly to face the floor surface to be cleaned. The dirt-bearing air is conveyed to the separating apparatus so that dirt and dust can be separated from the air before the air is expelled to the atmosphere. The separating apparatus can take the form of a filter, a filter bag or, as is known, a cyclonic arrangement.
Vacuum cleaners generally include cylinder, or canister, cleaners, upright cleaners and hand-held cleaners. A cylinder vacuum cleaner includes a main body supported by a set of wheels which is dragged along a floor surface by a hose and wand assembly extending between the main body and the cleaner head. The cleaner head is generally releasably attached to the end of the wand which is remote from the main body. An upright vacuum cleaner typically comprises a main body, a rolling assembly mounted on the main body for maneuvering the vacuum cleaner over a floor surface to be cleaned, and a cleaner head mounted on the main body. In use, a user reclines the main body of the upright vacuum cleaner towards the floor surface, and then sequentially pushes and pulls a handle which is attached to the main body to maneuver the vacuum cleaner over the floor surface.
A driven agitator, usually in the form of a brush bar, may be rotatably mounted within a brush bar chamber of the cleaner head. The brush bar comprises an elongate cylindrical core bearing bristles which extend radially outward from the core. The bristles are generally provided in clumps or tufts of bristles spaced about and along the core of the brush bar. The suction opening is located at the bottom of the brush bar chamber, and the brush bar is mounted within the chamber so that the bristles protrude by a small extent through the suction opening. An exhaust port of the brush bar chamber is generally located towards the rear of the brush bar chamber. The exhaust port is usually in the form of a circular or rectangular aperture formed in the brush bar chamber.
The brush bar is activated mainly when the vacuum cleaner is used to clean carpeted surfaces. Rotation of the brush bar about its longitudinal axis may be driven by an electric motor powered by a power supply derived from the main body of the cleaner, or by a turbine driven by an air flow passing through or into the cleaner head. The rotation of the brush bar causes the bristles to be swept between the fibers of the carpet to be cleaned, agitating both the fibers of the carpet and any debris, such as dust particles, fibers and hairs, located on the surface of the carpet and/or between the fibers of the carpet.
WO 2010/142968 describes a cleaner head having a brush bar bearing two different types of bristles which each protrude through the suction opening with rotation of the brush bar. The suction opening is located within a planar sole plate of the cleaner head. The brush bar has a number of rows of relatively stiff, short bristles arranged in a series of tufts regularly spaced along the rows, and a number of rows of relatively soft, long bristles which extend radially outwardly from the brush bar beyond the relatively short bristles. The cleaner head includes wheels which support the cleaner head on a floor surface so that when the cleaner head is located on a hard floor surface, the sole plate is spaced from that surface. A first plane containing the lowermost extremities of the wheels is parallel to a second plane containing the sole plate and the suction opening.
The lengths of the bristles are selected so that when the cleaner head is located on a hard floor surface, the relatively long bristles engage the floor surface whereas the relatively short bristles are spaced from the floor surface to prevent those bristles from marking the floor surface. When the cleaner head is moved on to a carpeted floor surface, the rolling elements sink between the fibers of the carpet to bring the sole plate and the relatively short bristles into contact with the carpet.
In order to improve the pick up performance of the cleaner head when it is located on a hard floor surface, it is desirable to locate the suction opening as close as possible to the floor surface. For example, the cleaner head may be designed so that the distance between the sole plate and the hard floor surface is no greater than 1 mm. In this case, the tips of the relatively short bristles must not protrude beyond the sole plate by a distance which is greater than 1 mm so that the relatively short bristles are spaced from the hard floor surface. This can require careful control of a number of the manufacturing parameters associated with the cleaner head so that they are within their prescribed engineering tolerances. These parameters include the length of the relatively short bristles, the distance between the rotational axis of the brush bar and the sole plate, the radius of the wheels, and the distance between the rotational axes of the wheels and the sole plate. The manufacture of the cleaner head and its various components to such tight engineering tolerances can increase significantly the cost of the cleaner head. On the other hand, if the cleaner head and its components are not manufactured to such tight tolerances, then there may be a relatively high rejection rate of manufactured cleaner heads on the production line, for example if the relatively short bristles do not protrude from the suction opening or if the relatively short bristles protrude from the opening beyond the first plane.